Plastic optical components

ABSTRACT

The invention concerns optical elements made from polycyanurate resins,  wh exhibit a refractive index, at 633 nm, in the range from 1.45 to 1.70 and an optical absorption, at 1.3 or 1.55 μm, in the range from 0.1 to 1.0 dB/cm.

FIELD OF THE INVENTION

The invention concerns optical elements made of plastic and inparticular those made from polycyanurate resins.

BACKGROUND OF THE INVENTION

Polymers are materials of increasing interest for optics, microoptics,integrated optics and microsystems engineering. They are therebyemployed in optical components as well as in special optics, such aslenses, prisms, for the fixing of optical systems, as substratematerials for optical coatings and as transparent coating material formirrors and lenses. Polymers can be utilized for optical fibers and forthe generation of waveguide structures. Their general advantage lies inthe favorable technological processability and their lower density incomparison with glass.

The application as waveguides, in particular, imposes manifold demandsupon the polymer. The refractive index should be as variable as possibleand capable of being adapted to certain substrates. In the case of anapplication in optical communications technology, small materialabsorptions at 1.3 and 1.55 μm are required. The absorption lossesresulting from volume defects (inhomogeneities, microbubbles) must beminimized. In addition to certain engineering requirements, such ascoating production and the ability to be structured, particularly thethermal and thermo-mechanical stability, adjusted expansion coefficientsand the very low degree of shrinkage are prerequisites for anapplication of polymers for waveguide structures in integrated optics.

The plastics thus far employed for optical applications arepolymethacrylates and polycarbonates. Their refractive index is however,at 1.49 or 1.58, relatively limited and not directly variable. Bothpolymer classes exhibit an excellent optical transparency but however,due to their chemical structure, are not particularly thermally andthermo-mechanically stable. Polycarbonate, for example, is thuspractically unusable at temperatures above 130° C. due to its relativelylow glass-transition range.

Other high-performance polymers exhibit glass-transition ranges (T_(g))of >180° C. Examples of these include polyaryl ether sulfones, polyarylsulfones, polyaryl ether ketones, polymides and polyether imides, which,compared with polymethacrylate and polycarbonate, are for the most parthowever more difficult to process. The application of these high-T_(g)polymers for optical systems is described is described in various patentdocuments, for example, in JP-A 61-144,738, JP-A 61-005,986, DE-A3,915,734, U.S. Pat. No. 4,477,555, EP-A 0,254,275, DE-A 3,429,074, DE-A3,927,498, DE-A 4,228,853, DE-A 3,636,399. A further disadvantage ofthese systems is the comparatively high optical absorption at thewavelengths of 1.3 and 1.55 μm relevant to communications technology.

The invention consequently addressed the problem of producing easilyworkable, thermally and thermo-mechanically stable polymers of variablerefractive index and low absorption at 1.3 and 1.55, which are suitablefor the manufacture of optical elements, as well as the optical elementsmanufactured from them.

SUMMARY OF THE INVENTION

This goal is achieved with an optical element of the type initiallydescribed, which is produced from a polycyanurate resin.

It was discovered, surprisingly, that polycyanurate resins areparticularly well suited for the manufacture of optical elements withthe desired properties cited above. These are for the most part knownproducts from conventional polycyanate raw materials, as they are widelyused in the plastics industry. Correspondingly, the starting materials,production processes and methods for processing these polycyanurateplastics are known.

DETAILED DESCRIPTION OF THE INVENTION

Particularly suitable for the invented optical elements arepolycyanurate resins which are obtained from the compounds shown below.##STR1## in which R¹ through R⁴, independently of each other, arehydrogen, C₁ -C₁₀ -alkyl, C₃ -C₈ -cycloalkyl, C₁ -C₁₀ -alkoxy, halogenor phenyl, in which case the alkyl or aryl groups can be fluorinated orpartially fluorinated, ##STR2## in which Z is a chemical bond, SO₂, CF₂,CH₂, CH(CH₃), isopropyl, hexafluoroisopropyl, C₁ -C₁₀ -alkyl, O, NR⁵,N═N, CH═CH, COO, CH═N, CH═N--N═CH, alkyloxyalkyl with C₁ -C₈ -alkyl, Sor ##STR3## where R⁵ is hydrogen or C₁ -C₁₀ -alkyl and n is 0 through20; as well as

dicyanates of a perhalogenated dihydroxyalkane IV, especially with up to10 carbon atoms,

as well as mixtures of the polycyanates with formulas I through IV.

The properties of the above-cited polycyanurate resins can be favorablyinfluenced, on the one hand, by employing them in mixtures, but, on theother, with phenols, for example, those having structure Va through Vc,in which R is hydrogen and R¹ through R⁵ are defined as above. ##STR4##aromatic glycide ethers with structure Va through c, in which R isglycidyl, or glycidyl anilines, for example, with basic structure VIathrough c. ##STR5## in which R₆ is N(R₇)₂ with R₇ glycidyl, and areconverted with complete hardening.

Such coreaction products with phenols, aromatic glycide ethers andglycidyl anilines are likewise well known. It is possible, for example,to obtain polycyanurate resins which, with regard to the polycyanate orpolycyanate mixture used, contain from 1 to 60 mol-% of phenol, from 1to 99 mol-% of glycide ether or from 1 to 99% of glycidyl aniline ormixtures of these components.

The polycyanurate resins employed per the invention have, in particular,a glass-transition temperature T_(g) of from 100° to 250° C.,particularly preferred from 180° to 250° C. Their refractive index at633 nm lies preferably in the range from 1.45 to 1.70, especiallypreferred in the range from 1.55 and 1.65.

Per the invention, optical absorptions in the range of from 0.1 to 1.0dB/cm can be achieved at 1.3 or 1.55 μm.

The polycyanurate resins are suitable for the manufacture of waveguidestructures, lenses, prisms, corrected lens systems, opticalphotoconductive fibers and substrates for optical coatings as well asfor the cementing of optical components and for fiber coupling, as wellas for numerous other purposes.

The employed polycyanurate resins can be obtained per the invention byemploying mixtures of various dicyanates in the polymer-formingreaction. The polycyanurates can be obtained furthermore by theconversion of dicyanates into the invented products in coreactions withphenols, aromatic glycide ethers or glycidyl anilines. The refractiveindex of the described polycyanurate resins can be varied and adjustedby the mixture of the monomer components in a wider range (1.45 to1.70). The polymers exhibit thermal stability at up to 250° C. Theglass-transition ranges of the invented resins lies between 100° and250° C., and in particular at >180° C.

The described resins exhibit very low optical losses at 1.3 and 1.55 μmin comparison with other high-Tg polymers, for example, polyimides. Theeasy processability of the invented materials results from the fact thatthey can be processed from the solution via spin-coating already in asoluble prepolymer stage, or from the meltings by means of stamping ormolding techniques. The polymers exhibit good adhesion to varioussubstrates. Final processing in the layer takes place by thermalhardening.

Subject matter of the invention is furthermore the use of polycyanurateresins, especially those defined in detail above, for the manufacture ofoptical elements.

The invention is explained in detail by means of the following examples.

EXAMPLE 1

100 g of dicyanate of bisphenol A (compound II with R₁ through R₄ =H,Z=isopropyl) are heated to 180° C., with agitation, under an inertatmosphere. The arising prepolymer is cooled after 350 min. It congealsas a transparent, amorphous, slightly yellowish mass. An OCN conversionof 41% is determined by means of IR spectrography.

The prepolymer is soluble in the conventionally used organic solvents.Films with a thickness range of from 1 to 10 μm are obtained from a 40%solution in hexanone by spin coating. After tempering and hardening ofthe layer at, finally, 200° C., a refractive index of 1.6095 at 633 nmis obtained. The optical absorption at 1.32 μm was 0.39 dB/cm, at 1.55μm, 1.1 dB/cm.

EXAMPLE 2

10 g of dicyanate of a substituted bisphenol A (compound II with R₁ -R₄=H, Z=hexafluoroisopropyl) are heated to 180° C. for 70 h until completehardening is achieved. The result is a transparent, amorphous, colorlessbody. The OCN conversion is determined by the use of IR spectroscopy.

The castings produced can be processed mechanically. End planes forcoupling in the laser beam are obtained by polishing. A refractive indexof 1.543 is determined at 663 nm. The optical absorption at 1.32 μm was0.6 dB/cm, at 1.55 μm, 0.7 dB/cm.

EXAMPLE 3

25 g of a substituted bisphenol A (compound II with R₁ -R₄ =CH₃, Z=CH₂)are heated to 180° C. for 80 h, until complete hardening is achieved.Obtained is a transparent, amorphous, yellowish body. The OCN conversionis detected using IR spectroscopy.

The casting produced can be precessed mechanically. End surfaces forcoupling in the laser beam are obtained by polishing. The refractiveindex determined at 633 nm is 1.579 (1.558 at 1.3 μm). The opticalabsorption at 1.32 μm was 0.6 dB/cm and 0.6 dB/cm at 1.55 μm.

EXAMPLE 4

7 g of dicyanate of a substituted bisphenol A (compound II with R₁ -R₄=CH₃, Z=CH₂) and 3 g of dicyanate of bisphenol A (compound II with R₁-R=H, Z=isopropyl) are heated to 120° C. for 92 h with the addition of2% of a catalyst, consisting of 200 parts of phenol and 1 part ofCu(acac)₂, until complete hardening. Obtained is a transparent,amorphous, yellowish body. The OCN conversion is ascertained by means ofIR spectroscopy.

The resulting casting can be worked by mechanical means. End surfacesfor coupling in a laser beam are produced by polishing. The refractiveindex at 633 nm is found to be 1.592.

EXAMPLE 5

3 g of dicyanate of a substituted bisphenol A (compound II with R₁ -R=H,Z=hexafluoroisopropyl) and 7 g of dicyanate of bisphenol A (compound IIwith R₁ -R₄ =H, Z=isopropyl) are heated to 120° C. for 92 h with theaddition of 2% of a catalyst, consisting of 200 parts of phenol and 1part of Cu(acac)₂, until hardening is complete. The result is atransparent, amorphous, slightly yellowish material. The OCN conversionis determined with IR spectroscopy.

The casting produced can be processed mechanically. End surfaces forcoupling in a laser beam are produced by polishing. The refractive indexdetermined at 633 nm is 1.592.

What is claimed is:
 1. An optical element comprising plastic, whereinsaid plastic is a polycyanurate resin.
 2. The optical element accordingto claim 1, wherein said polycyanurate resin is derived from at leastone polycyanate selected from the group consisting of ##STR6## whereinR¹ through R⁴, independently of each other, can be hydrogen, C₁ -C₁₀-alkyl, C₃ -C₈ -cycloalkyl, C₁ -C₁₀ -alkoxy, halogen or phenyl, in whichcase the alkyl or aryl groups can be fluorinated or partiallyfluorinated, ##STR7## wherein Z is a chemical bond, SO₂, CF₂, CH₂,CH(CH₃), isopropyl, hexfluoroisopropyl, C₁ -C₁₀ -alkyl, O, NR⁵, N═N,CH═CH, COO, CH═N, CH═N--N═CH, alkyloxyalkyl with C₁ -C₈ -alkyl, S or##STR8## where R⁵ is hydrogen or C₁ -C₁₀ -alkyl and n equals 0-20, andadicyanate of a perhalogenated dihydroxy alkane IV.
 3. The opticalelement of claim 1 wherein said polycyanurate resin is derived from abisphenol-A dicyanate.
 4. The optical element of claim 1, wherein saidpolycyanurate resins are coreaction products of the polycyanates withphenols, aromatic glycide ethers or glycidyl anilines.
 5. The opticalelement of claim 4, wherein said polycyanurate resins contain, relativeto the polycyanate used, from 1 to 60 mol-% of phenol, from 1 to 99mol-% of glycidyl ether or from 1 to 99 mol-% of glycidyl aniline. 6.The optical element of claim 1 wherein said polycyanurate resin exhibitsa glass-transition temperature of from approximately 100° C. toapproximately 250° C.
 7. The optical element of claim 1 wherein saidoptical element has a refractive index, at 633 nm, in the range of from1.45 to 1.70.
 8. The optical element of claim 1 wherein said opticalelement has an optical absorption, at 1.3 or 1.55 μm, in the range offrom 0.1 to 1.0 dB/cm.
 9. The optical element of claim 1 wherein saidoptical element is obtained by spin-coating the dissolved polycyanurateresin.
 10. The optical element of claim 1 wherein said optical elementis obtained from meltings by molding techniques.
 11. Optical element ofclaim 1 wherein the polycyanurate resin is thermally hardened.
 12. Theoptical element of claim 1 wherein said optical element is an opticaldevice selected from the group consisting of waveguide structures,lenses, prisms, corrected-lens systems, optical photoconductive fibers,substrates for optical coatings, and adhesives for optical components.13. The optical element of claim 2 wherein the dicyanate of aperhalogenated dihydroxy alkane has up to 10 carbon atoms.
 14. Theoptical element of claim 1 wherein said polycyanurate resin exhibits aglass-transition temperature of from approximately 180° C. toapproximately 250° C.
 15. The optical element of claim 1 wherein saidoptical element has a refractive index, at 633 nm, in the range of from1.55 to 1.65.
 16. The optical element of claim 1 wherein said opticalelement is obtained from meltings by stamping techniques.
 17. Theoptical elements of claim 11 wherein said polycyanurate resin has beenthermally hardened in the presence of a catalyst.